Biosynthesis of (S)-4-chloro-3-hydroxybutanoate ethyl using Escherichia coli co-expressing a novel NADH-dependent carbonyl reductase and a glucose dehydrogenase

Cloning, Expression and Characterization of a Highly Active Alcohol Dehydrogenase for Production of Ethyl (S)-4-Chloro-3-Hydroxybutyrate

A novel alcohol dehydrogenase from Bartonella apis (BaADH) was heterologous expressed in Escherichia coli. Its biochemical properties were investigated and used to catalyze the synthesis of ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE), which is a chiral intermediate of the cholesterol-lowering drug atorvastatin. The purified recombinant BaADH displayed 182.4 U/mg of the specific activity using ethyl 4-chloroacetoacetate as substrate under the conditions of 50 °C in pH 7.0 Tris-HCl buffer. It was stable in storage buffers of pH 7 to 9 and retains up to 96.7% of the initial activity after 24 h. The K _m and V _max values of BaADH were 0.11 mM and 190.4 μmol min^-1 mg^-1, respectively. Synthesis of (S)-CHBE catalyzed by BaADH was performed with a cofactor regeneration system using a glucose dehydrogenase, and a conversion of 94.9% can be achieved after 1 h reaction. Homology modeling and substrate docking revealed that a typical catalytic triad is in contact with local water molecules to form a catalytic system. The results indicated this ADH could contribute to the further enzymatic synthesis of (S)-CHBE.

Genome mining, in silico validation and phase selection of a novel aldo-keto reductase from Candida glabrata for biotransformation

Previously, we published cloning, overexpression, characterization and subsequent exploitation of a carbonyl reductase (cr) gene, belonging to general family aldo-keto reductase from Candida glabrata CBS138 to convert keto ester (COBE) to a chiral alcohol (ethyl-4-chloro-3-hydroxybutanoate or CHBE). Exploiting global transcription factor CRP, rDNA and transporter engineering, we have improved batch production of CHBE by trinomial bioengineering. Herein, we present the exploration of cr gene in Candida glabrata CBS138 through genome mining approach, in silico validation of its activity and selection of its biocatalytic phase. For exploration of the gene under investigation, 3 template genes were chosen namely Saccharomyces cerevisae YDR541c, YGL157w and YOL151w. The CR showed significant homology match, overlapping of substrate binding site and NADPH binding site with the template proteins. The binding affinity of COBE toward CR (-4.6 Kcal/ mol) was found higher than that of the template proteins (-3.5 to -4.5 Kcal/ mol). Biphasic biocatalysis with cofactor regeneration improved product titer 4∼5 times better than monophasic biotransformation. Currently we are working on DNA Shuffling as a next level of strain engineering and we demonstrate this approach herein as a future strategy of biochemical engineering.

Engineering Streptomyces coelicolor Carbonyl Reductase for Efficient Atorvastatin Precursor Synthesis

Streptomyces coelicolor CR1 (ScCR1) has been shown to be a promising biocatalyst for the synthesis of an atorvastatin precursor, ethyl-(S)-4-chloro-3-hydroxybutyrate [(S)-CHBE]. However, limitations of ScCR1 observed for practical application include low activity and poor stability. In this work, protein engineering was employed to improve the catalytic efficiency and stability of ScCR1. First, the crystal structure of ScCR1 complexed with NADH and cosubstrate 2-propanol was solved, and the specific activity of ScCR1 was increased from 38.8 U/mg to 168 U/mg (ScCR1_I158V/P168S) by structure-guided engineering. Second, directed evolution was performed to improve the stability using ScCR1_I158V/P168S as a template, affording a triple mutant, ScCR1_{A60T/I158V/P168S}, whose thermostability (T₅₀¹⁵, defined as the temperature at which 50% of initial enzyme activity is lost following a heat treatment for 15 min) and substrate tolerance (C₅₀¹⁵, defined as the concentration at which 50% of initial enzyme activity is lost following incubation for 15 min) were 6.2°C and 4.7-fold higher than those of the wild-type enzyme. Interestingly, the specific activity of the triple mutant was further increased to 260 U/mg. Protein modeling and docking analysis shed light on the origin of the improved activity and stability. In the asymmetric reduction of ethyl-4-chloro-3-oxobutyrate (COBE) on a 300-ml scale, 100 g/liter COBE could be completely converted by only 2 g/liter of lyophilized ScCR1_{A60T/I158V/P168S} within 9 h, affording an excellent enantiomeric excess (ee) of >99% and a space-time yield of 255 g liter^-1 day^-1 These results suggest high efficiency of the protein engineering strategy and good potential of the resulting variant for efficient synthesis of the atorvastatin precursor.IMPORTANCE Application of the carbonyl reductase ScCR1 in asymmetrically synthesizing (S)-CHBE, a key precursor for the blockbuster drug Lipitor, from COBE has been hindered by its low catalytic activity and poor thermostability and substrate tolerance. In this work, protein engineering was employed to improve the catalytic efficiency and stability of ScCR1. The catalytic efficiency, thermostability, and substrate tolerance of ScCR1 were significantly improved by structure-guided engineering and directed evolution. The engineered ScCR1 may serve as a promising biocatalyst for the biosynthesis of (S)-CHBE, and the protein engineering strategy adopted in this work would serve as a useful approach for future engineering of other reductases toward potential application in organic synthesis.

Effective asymmetric bioreduction of ethyl 4-chloro-3-oxobutanoate to ethyl (R)-4-chloro-3-hydroxybutanoate by recombinant E. coli CCZU-A13 in [Bmim]PF6-hydrolyzate media

It was the first report that the concentrated hydrolyzates from the enzymatic hydrolysis of dilute NaOH (3wt%)-soaking rice straw at 30°C was used to form [Bmim]PF6-hydrolyzate (50:50, v/v) media for bioconverting ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (R)-4-chloro-3-hydroxybutanoate [(R)-CHBE] (>99% e.e.) with recombinant E. coli CCZU-A13. Compared with pure glucose, the hydrolyzates could promote both initial reaction rate and the intracellular NADH content. Furthermore, emulsifier OP-10 (20mM) was employed to improve the reductase activity. Moreover, Hp-β-cyclodextrin (0.01mol Hp-β-cyclodextrin/mol COBE) was also added into this bioreaction system for enhancing the biosynthesis of (R)-CHBE from COBE by E. coli CCZU-A13 whole-cells. The yield of (R)-CHBE (>99% e.e.) from 800mM COBE was obtained at 100% in the [Bmim]PF6-hydrolyzate (50:50, v/v) media by supplementation of OP-10 (20mM) and Hp-β-CD (8mM). In conclusion, an effective strategy for the biosynthesis of (R)-CHBE was successfully demonstrated.

Effective pretreatment of sugarcane bagasse with combination pretreatment and its hydrolyzates as reaction media for the biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate by whole cells of E. coli CCZU-K14

In this study, sugarcane bagasse (SB) was pretreated with combination pretreatment (e.g., sequential KOH extraction and ionic liquid soaking, sequential KOH extraction and Fenton soaking, or sequential KOH extraction and glycerol soaking). After the enzymatic hydrolysis of pretreated SBs, it was found that all these three concentrated hydrolyzates could be used for the asymmetric bioreduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE]. Compared with glucose, arabinose and cellobiose couldn't promote the initial reaction rate, and xylose could increase the intracellular NADH content. Moreover, it was the first report that hydrolyzates could be used for the effective biosynthesis of (S)-CHBE (∼500g/L; 98.0% yield) from 3000 COBE by whole cells of Escherichia coli CCZU-K14 in the presence of β-CD (0.4mol β-CD/mol COBE), l-glutamine (200mM) and glycine (500mM). In conclusion, it is a new alternative to utilize bioresource for the synthesis of key chiral intermediate (S)-CHBE.

Improved biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate by adding L-glutamine plus glycine instead of NAD+ in β-cyclodextrin-water system

To reduce dependence on the expensive cofactor and effectively biotransform ethyl 4-chloro-3-oxobutanoate, L-glutamine and glycine were found to enhance the content of intracellular NADH and the reductase activity. Adding the mixture of 200 mM of L-glutamine and 500 mM of glycine to the reaction media, a 1.67-fold of reductase activity was increased over the control without the addition of the two compounds. Moreover, β-cyclodextrin (0.4 mol β-cyclodextrin/mol ethyl 4-chloro-3-oxobutanoate) was also added into this reaction media, and the biocatalytic activity of the whole-cell biocatalyst of Escherichia coli CCZU-K14 was increased by 1.34-fold than that without β-cyclodextrin. In this β-cyclodextrin-water media containing L-glutamine (200 mM) plus glycine (500 mM), ethyl (S)-4-chloro-3-hydroxybutanoate (>99% ee) could be obtained from 3000 mM ethyl 4-chloro-3-oxobutanoate in the yield of 98.0% after 8h. All the positive features demonstrate the potential applicability of the bioprocess for the large-scale production of ethyl (S)-4-chloro-3-hydroxybutanoate.

Asymmetric synthesis of (S)-4-chloro-3-hydroxybutanoate by sorbose reductase from Candida albicans with two co-existing recombinant Escherichia coli strains

An NADPH-dependent sorbose reductase from Candida albicans was identified to catalyze the asymmetric reduction of ethyl 4-chloro-3-oxobutanoate (COBE). The activity of the recombinant enzyme toward COBE was 6.2 U/mg. The asymmetric reduction of COBE was performed with two coexisting recombinant Escherichia coli strains, in which the recombinant E. coli expressing glucose dehydrogenase was used as an NADPH regenerator. An optical purity of 99% (e.e.) and a maximum yield of 1240 mM (S)-4-chloro-3-hydroxybutanoate were obtained under an optimal biomass ratio of 1:2. A highest turnover number of 53,900 was achieved without adding extra NADP(+)/NADPH compared with those known COBE-catalytic systems.

Biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate with an NADH-dependent reductase (ClCR) discovered by genome data mining using a modified colorimetric screening strategy

An NADH-dependent reductase (ClCR) was discovered by genome data mining. After ClCR was overexpressed in E. coli BL21, recombinant E. coli CCZU-T15 with high reductase activity and excellent stereoselectivity for the reduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE] was screened using a modified high-throughput colorimetric screening strategy. After the reaction optimization, a highly stereoselective bioreduction of COBE into (S)-CHBE (>99% ee) with the resting cells of E. coli CCZU-T15 was successfully demonstrated in toluene-water (50:50, v/v) biphasic system. Biotransformation of 1000 mM COBE for 24 h in the biphasic system, (S)-CHBE (>99% ee) could be obtained in the high yield of 96.4%. Significantly, E. coli CCZU-T15 shows high potential in the industrial production of (S)-CHBE (>99% ee).

Discovery of a reductase-producing strain recombinant E. coli CCZU-A13 using colorimetric screening and its whole cell-catalyzed biosynthesis of ethyl (R)-4-chloro-3-hydroxybutanoate

An NADH-dependent reductase (SsCR) was discovered by genome data mining. After SsCR was overexpressed in E. coli BL21, recombinant E. coli CCZU-A13 with high reductase activity and excellent stereoselectivity for the reduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (R)-4-chloro-3-hydroxybutanoate ((R)-CHBE) was screened using one high-throughput colorimetric screening strategy. After the reaction optimization, a highly stereoselective bioreduction of COBE into (R)-CHBE (>99% ee) with the resting cells of E. coli CCZU-A13 was successfully demonstrated in n-butyl acetate-water (10:90, v/v) biphasic system. Biotransformation of 600mM COBE for 8h in the biphasic system, (R)-CHBE (>99% ee) could be obtained in the high yield of 100%. Moreover, the broad substrate specificity in the reduction of aliphatic and aromatic carbonyl compounds was also found. Significantly, E. coli CCZU-A13 shows high potential in the industrial production of (R)-CHBE (>99% ee) and its derivatives.

Highly efficient synthesis of ethyl (S)-4-chloro-3-hydroxybutanoate and its derivatives by a robust NADH-dependent reductase from E. coli CCZU-K14

An NADH-dependent reductase (CmCR) from Candida magnoliae was discovered by genome mining for carbonyl reductases. After CmCR was overexpressed in Escherichia coli BL21, a robust reductase-producing strain, recombinant E. coli CCZU-K14, was employed for the efficient synthesis of ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE) from the reduction of ethyl 4-chloro-3-oxobutanoate (COBE). After the optimization, the optimum reaction conditions were obtained. Notably, E. coli CCZU-K14 had broad substrate specificity in reducing both aliphatic and aromatic substrates, and excellent enantioselectivity of CCZU-K14 was observed for most of the tested substrates, resulting in chiral alcohols of over 99.9% ee. Moreover, COBE at a high concentration of (3000mM) could be asymmetrically reduced to (S)-CHBE in the high yield (>99.0%) and high enantiometric excess value (>99.9% ee) after 14h. Significantly, E. coli CCZU-K14 shows high potential in the industrial production of (S)-CHBE and its derivatives (>99.9% ee).

Production of (3S)-acetoin from diacetyl by using stereoselective NADPH-dependent carbonyl reductase and glucose dehydrogenase

Production of (3S)-acetoin ((3S)-AC), an important platform chemical, is desirable but difficult to perform. An NADPH-dependent carbonyl reductase (Gox0644) from Gluconobacter oxydans DSM 2003 was confirmed to have a good ability to reduce diacetyl (DA) to produce (3S)-AC. In this work, the NADPH-dependent carbonyl reductase was expressed and purified. Glucose dehydrogenase from Bacillus subtilis 168 was coupled with the NADPH-dependent carbonyl reductase to produce (3S)-AC from DA. Under the optimal conditions, 12.2 g l(-1) (3S)-AC was produced from 14.3 g l(-1) DA in 75 min. Because DA can be biotechnological produced, the two-enzymes coupling system might be a promising alternative for the (3S)-AC production.

Recent trends in biocatalysis engineering

During the last 30 years the scope of biocatalysis has been expanding due to the advances in several technological fields. Diverse techniques as structural enzyme improvement (e.g. protein engineering, direct evolution), engineering approaches (e.g. ionic liquids, supercritical fluids) and physical stabilization (e.g. immobilization, CLEAS) have been developed, which in combination are powerful tools to improve biotransformation and to synthesize new products. In the present work, recent advances in biocatalysis are reviewed.

A novel reductase from Candida albicans for the production of ethyl (S)-4-chloro-3-hydroxybutanoate

A novel NADPH-dependent reductase (CaCR) from Candida albicans was cloned for the first time. It catalyzed asymmetric reduction to produce ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE). It contained an open reading frame of 843 bp encoding 281 amino acids. When co-expressed with a glucose dehydrogenase in Escherichia coli, recombinant CaCR exhibited an activity of 5.7 U/mg with ethyl 4-chloro-3-oxobutanoate (COBE) as substrate. In the biocatalysis of COBE to (S)-CHBE, 1320 mM (S)-CHBE was obtained without extra NADP+/NADPH in a water/butyl acetate system, and the optical purity of the (S)-isomer was higher than 99% enantiomeric excess.

Purification and characterization of a novel NADH-dependent carbonyl reductase from Pichia stipitis involved in biosynthesis of optically pure ethyl (S)-4-chloro-3-hydroxybutanoate

A novel NADH-dependent dehydrogenases/reductases (SDRs) superfamily reductase (PsCRII) was isolated from Pichia stipitis. It produced ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE] in greater than 99% enantiomeric excess. This enzyme was purified to homogeneity by ammonium sulfate precipitation followed by Q-Sepharose chromatography. Compared to similar known reductases producing (S)-CHBE, PsCR II was more suitable for production since the purified PsCRII preferred the inexpensive cofactor NADH to NADPH as the electron donor. Furthermore, the Km of PsCRII for ethyl 4-chloro-3-oxobutanoate (COBE) was 3.3 mM, and the corresponding Vmax was 224 μmol/mg protein/min. The catalytic efficiency is the highest value ever reported for NADH-dependent reductases from yeasts that produce CHBE with high enantioselectivity. In addition, this enzyme exhibited broad substrate specificity for several β-keto esters using NADH as the coenzyme. The properties of PsCRII with those of other carbonyl reductases from yeasts were also compared in this study.